There is increasing evidence that P300, a late positive component of the event-related potential (ERP) is reduced in amplitude in schizophrenics. In this project, the cognitive, affective and clinical implications of this reduction will be investigated. First, a series of experiments comparing Research Diagnostic Criteria (RDC)-positive schizophrenics and age and educationally matched normals will be performed to test hypotheses regarding why P300 is reduced in schizophrenics: deficits in selective attention, failure to apprehend sequential probability, general loss of reactivity, and poor reaction time (RT) performance. in addition, the usefulness of measures of P300 latency in detecting deficits in stimulus evaluation with increasing stimulus complexity will be investigated. Clinical measures of formal thought disorder, affective hyporeactivity and depressed mood will be correlated with P300 and RT measures. The diagnositic specificity of P300 reduction will be investigated in a second series of experiments, in which a third comparison group, patients meeting the RDC for major depressive disorder, will be added. Paradigms providing the clearest discrimination between schizophrenics and controls in the first series will be used in the second series. Hypothesis stating that P300 reduction is related to symptoms such as affective hyporeactivity, formal thought disorder, or poor behavioral task performance rather than to diagnostic category will be tested.